Clever Apes #24: Gut feelings

Scientists say the intestines are like a second brain. (WBEZ/Michael De Bonis)

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In researching the human gut over the last few weeks, I’ve learned at least 10 things that have blown my mind. Here is one: Your intestines are your second brain.

The gut has its own nervous system – called the enteric nervous system – that is highly sophisticated and can basically think for itself. Columbia University neuroscientist Michael Gershon, who coined the phrase with his 1999 book The Second Brain, says the gut can function just fine in a decapitated person.

Rush's Ali Keshavarzian with his colon model. (WBEZ/Gabriel Spitzer)

In fact, you can pull the gut out of someone, drop it in a nutrient bath in a lab, and it goes right on digesting.

In the last few years scientists have been discovering all kinds of surprising connections between the brain in your belly and the one in your head. Many neurological conditions also have gastro-intestinal components, though it’s never been clear why. The assumption has been that the brain disease causes the G-I problems, but scientists at Rush University Medical Center are investigating a hypothesis that would turn that theory upside down.

It goes like this: Parkinson’s disease patients seem to have unusually leaky intestines, which let toxic materials, like pieces of gut bacteria, slip between the cells lining the intestines. It’s possible that this could inflame the nerves and cause a particular protein, called alpha synuclein, to fold up wrong. That in turn could trigger a chain reaction of misfolded proteins that travel up the nervous system, burning “like a slow fuse” up to the brain over the course of decades, eventually causing Parkinson’s disease.

It’s still pretty speculative, but gut leakiness has now been linked with a bunch of other neurological diseases. In general, the gut and the trillions of bacteria that live there are turning up as strong candidates to account for correlations that have eluded explanation.

For example, scientists have long suspected that weight gain increases one's risk of breast cancer, but the reason why has been mysterious. Stay tuned for more on why gut bacteria could be the missing link: We’ll post an interview in a couple of days.

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Meanwhile, elsewhere in today’s episode we have a cautionary tale about what happens when we fail to respect the needs of our inner bug civilization. Antibiotics, in addition to killing infectious bacteria, also take a toll on our healthy gut biota, leaving room for an aggressive bug called Clostridium difficile. It causes an absolutely miserable, sometimes lethal, hospital-acquired infection that is reaching epidemic proportions in the U.S. It’s bad enough that some have turned to a particularly stomach-turning therapy: fecal transplants. Researchers at Loyola University Medical Center and the Hines VA in Maywood, Ill. are trying to save you from having to even think about that. We visit them and find out how.

Believe me, I could go on … but I’ll spare you for now. As always, subscribe to our podcast, follow us on Twitter, and find us on Facebook.